1. Field of the Invention
This invention relates to a constant running speed control system for automatically controlling the running speed of a vehicle provided with an engine at a constant speed.
2. Description of the Prior Art
Hitherto, there have been proposed various vehicle running speed control systems, and recently those using fluid actuators for causing displacement of vehicle speed adjustment elements have been attracting attention. The main reasons for this are that the actuator is inexpensive in cost and particularly in case of a vehicle using an internal combustion engine as the drive power source it is possible to make use of the intake negative pressure as the operating pressure. Generally, however, the fluid actuator has drawbacks in that a delay time is involved in its response to a control command. Besides, restrictions are imposed upon the utility of the engine intake negative pressure in order to prevent deterioration of the engine combustion performance. The problem of the delay of the response of the actuator has not been solved so far as the construction of the actuator itself is concerned.